The present invention is directed to methods and apparatus for reconstructing a portion of a surface of an organ from location data of a plurality of points on the organ surface. The invention is particularly directed at three-dimensional reconstruction of a portion of a surface of a heart chamber.
A number of techniques have been proposed for reconstructing the surface of a body organ based on location data of sample points on or near the organ surface. One such technique is disclosed in U.S. patent application Ser. No. 09/122,137 and in its corresponding European Patent Application 974,936 filed on Jul. 23, 1999. In a preferred embodiment of the ""137 application, an initial, closed 3D curve, preferably, an ellipsoid, is defined in the volume of the sampled points. The initial closed curve either encompasses most of the sample points or is interior to substantially all of the points. A grid of desired density is defined on the curve and the curve is adjusted by adjusting the grid points to resemble the configuration of the organ surface. The technique of the ""137 application works well for reconstructing a chamber of a heart where ample location data has been collected at representative points on the chamber surface.
The method of the ""137 has been proposed for reconstructing a map of the heart chamber which, in addition to depicting chamber geometry, also shows a physiological property of the tissue in the chamber. Illustrative physiological properties include electrical properties such as local activation time or peak voltage, or mechanical properties such as tissue contractility. The resultant maps may be used for directing therapy to specific tissue that harbors a particular pathology.
Cardiologists are increasingly looking to shorten the duration of cardiac procedures, including electrophysiology procedures. Also, cardiologists have access to other modalities that allow them to diagnose pathology and localize it to a particular region or area of interest in the heart. Thus, in many cases, it is no longer necessary to reconstruct a map of the entire cardiac chamber based on data sampled throughout the chamber. Rather, it is desirable to provide diagnostic methods which permit the reconstruction of only a portion of a surface of an organ. Unfortunately, the method of the ""137 application does not always accurately reconstruct the surface of a portion of the organ absent representative data taken throughout the organ. Thus, there exists a need for methods and apparatus which allow for accurate reconstruction of areas of interest within an organ without reconstructing the organ as a whole.
One aspect of the present invention is directed to a method of generating a three-dimensional reconstruction of a portion of a surface of an organ. The reconstruction is generated from location data of a plurality of acquisition points on the organ surface. Each of the acquisition points has a three-dimensional location on the organ surface. The method comprises computing a two-dimensional reference plane based on the location data. A function that describes the surface is then computed, wherein each point on the surface may be described as a function of the reference plane. The function is then bounded to a constrained region.
The reference plane generated by the method of the invention exhibits errors with respect to the three-dimensional locations of the acquisition points. In some embodiments, the plane is computed by minimizing the errors from the acquisition points to the plane.
In some embodiments, the plane is computed by minimizing the mean square error between the acquisition points and the plane.
In some embodiments, in minimizing the errors from the plane to the acquisition points, the errors are weighted. In one weighting scheme, higher weights are accorded to isolated location data points.
In some embodiments, the plane calculated in the method of the invention passes through the center of a bounding ellipsoid surrounding the acquisition points. In other embodiments, the plane passes through the center of mass of a convex hull of the acquisition points. In still other embodiments, the plane passes through the center of mass of the acquisition points.
In some embodiments, the function calculated in the method of the invention passes through the acquisition points. Exemplary functions are splines and radial basis functions. Alternatively, the function may be a piecewise linear function, formed, for example, by triangulation of the location data points.
In some embodiments, the value of the function corresponding to a point on the plane is a weighted average of the locations of the acquisition points. One way of weighting the acquisition points in calculating the value of the function is to weight the acquisition points by their respective distances from that point on the plane.
In some embodiments of the method of the invention, the function is bounded by a convex hull of the projection of the location data points onto the plane.
In some embodiments, the method of the invention may comprise tessellating the function. Where the function is tessellated, in some embodiments, vertices of the tessellation may be made to coincide with at least some of the location data points. Tessellation may be performed, for example, by Delaunay triangulation of the reference plane.
The method of the invention may further comprise refining the tessellation by adding virtual points to the surface. The value of the virtual points may be determined from the function.
Another embodiment of the method of the invention comprises computing a two-dimensional reference plane based on the location data. A function that describes the surface is then computed, wherein each point on the surface may be described as a function of the reference plane. The function is then tessellated.
In some embodiments, for example, when the tessellation is performed by Delaunay triangulation, the tessellation also serves to bound the function to a constrained region.
In some embodiments, the method of the invention further comprises displaying the reconstruction.
In some embodiments, the location data used in the method of the invention may be associated with data characteristic of a property of the tissue at the acquisition points. In that case, the method of the invention may further comprise displaying the reconstruction, wherein the reconstruction comprises geometrical information as well as tissue property information of the data acquisition points. The reconstruction may further comprise property information intermediate the acquisition points. The reconstruction may be colored so as to indicate the value of the property information.
In some embodiments, the method of the invention is directed to generating a reconstruction of a portion of the surface of a heart.
The location data used in the method of the invention may be acquired with a catheter comprising a position sensor. In some embodiments, the position sensor is an electromagnetic position sensor.
Another aspect of the invention is directed to apparatus for generating a three-dimensional reconstruction of a portion of a surface of an organ from location data of a plurality of acquisition points on the organ surface. Each of the acquisition points has a three-dimensional location on the organ surface. In one embodiment, the apparatus of the invention comprises a computer processor which computes a two-dimensional reference plane based on the location data. The processor then computes a function that describes the surface, wherein each point on the surface may be described as a function of the reference plane. The processor then bounds the function to a constrained region.
In another embodiment of the apparatus of the invention, the processor computes a two-dimensional reference plane based on the location data. The processor then computes a function that describes the surface, wherein each point on the surface may be described as a function of the reference plane. The processor than tessellates the function. In some embodiments, such as where tessellation is performed by Delaunay triangulation of the reference plane, the tessellation serves to bound the function to a constrained region.
In some embodiments of the invention, the instructions for the computer processor are embodied in computer software.
In some embodiments, the apparatus of the invention further comprises dedicated graphics circuitry which may perform some of the above-named tasks of the computer processor as well as additional calculations involved in displaying the reconstruction.
In some embodiments, the apparatus of the invention further comprises a display.
In some embodiments of the apparatus of the invention, location data of each of the acquisition points is associated with data characteristic of a property, such as an electrical property, of tissue at the points. In such a case, the apparatus of the invention may provide a reconstruction which represents both the geometry and the tissue property of the portion of the organ.
In some embodiments, the apparatus of the invention further comprises a catheter, the catheter comprising at least one electrode and at least one position sensor. In some embodiments, the at least one position sensor comprises an electromagnetic position sensor.